Radios, computers, and other electronic equipment often generate electromagnetic signals in one portion of the electronic equipment which may radiate to and interfere with another portion of the electronic equipment. To minimize this interference effect, electrically conducting (and sometimes magnetically conducting) material is interposed between the two portions of the electronic circuitry. This shielding may take the form of a wall or a complete enclosure and may be placed around the portion of the electronic circuit generating the electromagnetic signal and/or may be placed around the portion of the electronic circuit which is susceptible to the electromagnetic signal.
Existing electromagnetic shields are typically formed from a sheet of metallic material having a plate member suitable for positioning above a circuit component element (or entire circuit), and includes side flange portions extending downwardly therefrom to cover side portions of the circuit component element. In order to function properly, the shield must be electrically coupled to the electrical circuit over which the shield is positioned. Therefore, one-piece shields are usually soldered to the electronic circuit in a position where it will perform a shielding function; unfortunately, such a permanent attachment is difficult to remove if the need for service arises.
To avoid permanent attachment, other electromagnetic shielding efforts include multiple components utilizing spring fingers and spring-like flanges to produce contact with one another. In order for these shields to function optimally, multiple contact points between shield components must be maintained. "U"-shaped double cantilever spring channels, like those disclosed in U.S. Pat. No. 4,890,199, allow both removable shields or raised areas of the housing to clip into the spring channels; however, additional circuit board area is required to employ the numerous channels that retain the removable shield or raised housing area. Another variation includes shields having removeable lids with angled spring-like flanges that allow tight attachment to walls extending from the circuit board. Although removeable, the flanges must be lengthy and the walls high in order to permit secure attachment. Circuit boards having electromagnetic shield assemblies of this type require an increase in the volume of the chassis housing the circuit board.
Thus, miniaturized electronic devices place even greater constraints on shielding, first, because the electronic circuits are closer together, and second, the physical room available for shielding is greatly reduced. The techniques for attaching or surrounding the electronic circuit by the shielding must consume as little space as possible while providing secure, easily manufactured, and easily repairable interconnections.
Therefore, a need exists for a method and apparatus for shielding an electrical circuit that emits, or is sensitive to, electromagnetic energy while requiring significantly less height than assemblies of the prior art and while facilitating easy access to the electrical circuit when necessary.